Vacuum-type circuit interrupter with pressure-monitoring means



Sept. 24, 1968 D. w. CROUCH Filed March 17, 1966 .C W n e w x M Y 5 aATTORNEY United States Patent 3,403,297 VACUUM-TYPE CIRCUIT INTERRUPTERWITH PRESSURE-MONITORING MEANS Donald W. Crouch, Newtown Square, Pa.,assignor to General Electric Company, a corporation of New York FiledMar. 17, 1966, Ser. No. 535,078 6 Claims. (Cl. 31762) This inventionrelates to means for monitoring the pressure inside a vacuum-typeaircraft interrupter and, more particularly, relates to monitoring meanscapable of performing its intended pressure-monitoring function evenwhile the interrupter is connected for service in a high voltage powercircuit.

A typical vacuum-type circuit interrupter comprises a highly evacuatedenvelope and a pair of relatively movable contacts located within theenvelope. When the interrupter is in closed position, the contacts areengaged and are thus capable of carrying current through theinterrupter. Circuit interruption is effected by separating the contactsto draw an arc therebetween, soon after which the arc is extinguishedand prevented from reigniting 'by the action of the vacuum.

To assure that the arc will be extinguished and prevented fromreigniting in the desired manner, it is important that the pressureinside the envelope be maintained below a predetermined value.

An object of my invention is to provide monitoring means which iscapable of monitoring this pressure while the interrupter is in serviceand which requires no vacuum seals or leads projecting into the envelopebeyond those already present without the monitoring means.

Another object is to provide monitoring means of this type which willnot impair the circuit-interrupting performance of the interrupter.

In carrying out the invention in one form, I provide a vacuum-typecircuit interrupter that comprises an evacuated envelope, a pair ofrelatively removable contacts inside the envelope, and a tubular metalshield surrounding the contact and normally isolated from the contactsby evacuated space inside the envelope. The pressure inside the envelopeis monitored by monitoring means comprising means for applying a highpotential across the evacuated space between the shield and saidcontacts when the interrupter is closed. This potential is suflicientlylow that no significant discharge is present across said space when thepressure inside the envelope is in a normal range but is sufiicientlyhigh to initiate a discharge across the space when the pressure insidesaid envelope is above the normal range. Current-responsive alarm orprotective means is provided in circuit with said highpotential-applying means for operating in response to the initiation ofsuch a discharge across said space. Means responsive to initiation of aninterrupter-opening operation is provided for removing said highpotential from across said space when an interrupter-opening operationis initiated and for reapplying said high potential across said spacewhen said interrupter is closed.

For a better understanding of the invention, reference may be had to thefollowing description taken in conjunction with the accompanyingdrawing, wherein:

FIG. 1 is a schematic illustration of one embodiment of the inventionshowing the vacuum interrupter whose pressure is being monitored in theclosed-circuit position.

FIG. 2 is a view similar to that of FIG. 1 except showing theinterrupter in the open-circuit position.

Referring now to FIG. 1, there is shown a vacuumtype circuit interrupterthat comprises a highly evacuated envelope 10 comprising a tubularcasing 11 of suitable insulating material and a pair of metal end caps12 and 13 closing olf the ends of the casing. Suitable seals 14 areprovided between the end caps and the casing to render the envelopevacuum-tight.

Located within the envelope 10 is a pair of separable disc-shapedcontacts 17 and 18 shown in their engaged, or closed-circuit, position.The upper contact 17 is a stationary contact suitably secured to aconductive rod 17a, which at its upper end is united to the upper endcap 12. The lower contact 18 is a movable contact joined to a conductiveoperating rod 1811 which is suitably mounted for vertical movement. Theoperating rod 18a projects through an opening in the lower end cap 13,and a flexible metallic bellows 20 provides a seal about the rod 18a to.allow for vertical movement of the rod without impairing the vacuuminside the envelope 10. As shown in FIG. 1, the bellows 20 is secured bysuitable seals at its respective opposite ends to the operating rod 18aand the end cap 13.

A basic function of the interrupter is to control the flow of anelectric current through a high voltage power circuit in which it isconnected. Such a circuit comprises a conductor 25 which is connected tothe upper end of contact rod 170, and a conductor 26 which is connectedto the lower end of contact rod 18a. When the contacts are in theirclosed position shown, current can flow between the conductors 25 and 26via the parts 17a, 17, 18, 18a of the interrupter.

Circuit interruption is effected by driving the lower contact rod 18adownwardly to separate the contacts 17 and 18. This establishes an arebetween the contacts, which persists until the first natural currentzero, assuming an alternating current circuit. The are is prevented fromreigniting after current zero by the high dielectric strength of thevacuum, thereby completing the interruption.

For condensing the metallic vapors that are liberated from the contactsby arcing, a tubular metal shield 30 is provided. Metal vapors projectedby the are from the gap between the contacts 17, 18 are intercepted andquickly condensed by this shield 30 during an interrupter operation.During an interrupter operation, as will soon be explained, this metalshield 30 is electrically isolated from both contacts 17 and 18. Theshield 30 is suitably supported on an annular metal disc 32 that extendsthrough the insulating casing 11 and is sealed to the insulating casing11 by suitable vacuum-tight seals at its opposite sides.

For driving the movable contact 18 downwardly to initiate theabove-described circuit interrupting operation, an insulating operatingrod, or input member 35 is provided. This insulating operating rod 35 isbiased in a downward direction by an opening spring 36, but it isnormally restrained in its elevated position shown by means of aconventional trip latch 38. When the latch 38 is released, the openingspring 36 quickly expands and thus drives the rod 35 downwardly. Asuitable stop 34 terminates this downward movement after a predeterminedtravel.

During the initial part of the opening operation, the rod 35 movesdownwardly through a limited amount of lost motion travel withoutcausing any downward motion of the movable contact 18. During thisinitial period the movable contact 18 is being held in engagement withthe stationary contact 17 by means of a wipe spring 39. Upon completionof this lost motion travel, a shoulder 40 on insulating rod 35 strikesan annular abutment 42 carried by the contact rod 18a. When this occurs,the movable contact 18 is quickly driven out of engagement with thestationary contact 17, thereby establishing the above-described arcbetween the contacts, soon after which the arc is extinguished. v

To assure that the arc will be extinguished in the desired manner, it isimportant that the static pressure inside the envelope be maintainedbelow a predetermined level. Typically, this level is about millimetersof mercury. I have provided monitoring means 50 which is capable ofcontinuously checking this pressure and of initiating appropriateprotective steps should the pressure rise above the preselected level.In the illustrated embodiment, these protective steps comprise settingoff an alarm and blocking a subsequent opening operation of theinterrupter, as will soon be explained.

The monitoring means 50 comprises a suitable source 51 of high potentialand a detector circuit comprising leads 52 and 54 connected across thesource 51 for applying the high potential of the source between theshield 30 and one of the contact rods 17a. This high potential is, ineffect, applied across the evacuated space 53 between the shield 30 andthe conductive structure 12, 17a, 17, 18, 18a, 20, 13 that iselectrically connected to the contact rod 17a. In one embodiment of theinvention, the voltage applied by the high potential source is in theneighborhood of 10 to 15 kv. If a normal vacuum is present in theinterrupter, i.e., a vacuum of about 10* millimeters of mercury orlower, no significant current flows across the evacuated space 53between the leads 52 and 54. The high dielectric strength of the vacuumin the evacuated space 53 prevents any such current flow. But shouldpressure in the envelope rise to about l0 millimeters of mercury orslightly higher, a glow discharge will be initiated between the shield30 and a portion of the conductive structure 12, 17a, 17, 18, 18a, 20,13. Current immediately flows between the leads 52 and 54 through thisdischarge inside the envelope.

For sensing this current, I provide a detector 60 in the form of asensitive current-responsive trip device that has a coil 62 connected inseries with the leads 52, 54. When the coil 62 is energized by currentexceeding a predetermined value, it operates an armature 63 to the leftagainst a biasing spring 64, thereby releasing a latch 66 to effecttripping of an auxiliary switch 65. This auxiliary switch 65 includesthree sets of contacts that are mechanically coupled together. The firstset of contacts is a normally closed set 68 connected in series withcoil 62 of the detector 60. The second set of contacts is anormally-open set 70 that is used for setting off an alarm when closed.The third set is a normally closed set of interlock contacts 72 that isconnected in series with a coil 74 of the trip latch 38 for theinterrupter.

When the latch 66 of the auxiliary switch 65 is released by thecurrent-responsive detector 60, a spring 76 on the auxiliary switchoperates the auxiliary switch 65, thereby opening contacts 68 and 72 andclosing contacts 70. The closing of contacts 70 completes a circuit foran alarm A, thereby giving a warning that the pressure inside theenvelope has risen to an undesirably high level.

The above-described opening of contacts 68 interrupts .any currentflowing through the detector circuit 52, 54, thereby terminating theelectrical discharge inside the envelope 10. By quickly terminating theelectrical discharge in this manner, I am able to prevent theinterrupter from being damaged by the discharge. A continuing dischargenot only could damage the interrupter but could set off a chain ofevents that could lead to damage to more expensive equipment associatedwith the interrupter. For limiting the current that flows through thedischarge, a suitable current-limiting resistor 79 is connected in thedetector circuit 52, 54.

Opening of the interlock contacts 72 serves to prevent the vacuuminterrupter from being tripped open when the pressure inside theenvelope 10 is at an undesirably high level. In this connection, openingof the contacts 72 effectively isolates the trip coil 74 from its sourceof tripping power. Opening of the interrupter is normally effected byclosing an opening-control switch 80; but with the interlock contacts 72open, closing of the switch 80 is no longer elfective to initiate aninterrupter-opening operation. Thus. when the pressure in the envelope10 rises to an undesirably high level, the interlock contacts 72 open toprevent tripping-open of the interrupter.

An important feature of my monitoring means is that its presence willnot impair the circuit-interrupting ability of the vacuum interrupterv Iprevent any such impairment of the interrupting ability by providing aswitch 95* in series with the lead 54 of the detector circuit 52, 54. Asshown in FIG. 1, this switch is closed when the interrupter is closed.But just prior to separation of the contacts 18, 17 during aninterrupter-opening operation the switch 90 is opened, thereby removingthe high potential of the source 51from the space 53 between shield 30and the contact structure. FIG. 2 shows the parts after such an openingoperation of the interrupter. By removing this high potential, theshield 30 is free to assume a floating potential intermediate that ofthe two contacts during interruption. This floating relationship of theshield 30 with respect to the contacts contributes to the interruptingability of the interrupter, and I am able to preserve this floatingrelationship despite the presence of monitoring means 50. v

It is to be noted that switch 90 is opened during an interrupter-openingoperation before the contacts 17, 18 actually separate. This earlyopening of switch 90 is advantageous because it allows the shield 34 toassume its floating relationship during the entire interruptingoperation.

For achieving early opening of the switch 90, I utilize the abovedescribed lost motion of insulating operating rod 35. As abovedescribed, the insulating operating rod 35 moves downwardly apredetermined initial distance before its shoulder 40 engages abutment42 to initiate separation of the contacts 17, 18. A cam 92 is connectedto the insulating operating rod 34, and downward motion of the rod 35moves this cam 92 sufficiently to cause switch 90 to open before thecontacts 17 and 18 of the interrupter part.

It should be noted that my monitoring means 50 requires no vacuum sealsor leads projecting into the evacuated envelope 10 beyond those alreadypresent without the monitoring means. In this respect, the vacuuminterrupter itself is of a conventional design. In this conventionaldesign, the contact rod 17a and the supporting disc 32 for the shield 30are exposed to the exterior of the envelope whether or not themonitoring means is present. By connecting the leads 52, 54 of mymonitoring means to these parts 17a and 32, I am able to obviate theneed for additional seals or leads beyond those already present.

It should be further noted that my monitoring means 50 is available tomonitor the pressure in the vacuum interrupter even while theinterrupter is connected for service in the high voltage circuit 25, 26.This monitoring function can continue without interrupt-ion so long asthe interrupter is closed. It is only when the interrupter is opened orwhen the pressure rises to an abnormally high value that monitoring isdiscontinued.

When it is desired to return the interrupter 10 from its open positionof FIG. 2 to its closed position of FIG. 1, the operating rod 35 isdriven upwardly by suitable closing means (not shown); and such movementreengages contact 18 with contact 17. Upward movement of the operatingrod 35 also recloses the switch 90, thus reapplying the voltage ofsource 51 to the space 53 inside the interrupter to resume monitoring.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects; and I, therefore intend in theappended claims to cover all such changes and modifications as fallwithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination,

(a) a vacuum-type circuit interrupter comprising an evacuated envelope,a pair of relatively movable contacts inside the envelope, and a tubularmetal shield surrounding the contacts and electrically isolated fromsaid contacts when the interrupter is closed by evacuated space insidesaid envelope,

(b) means for monitoring the pressure inside said evacuated envelopewhile the interrupter is carrying current therethrough, comprising:

(i) high potential-applying means for applying a high potential acrosssaid space between said shield and said contacts when the interrupter isclosed,

(ii) said potential being sufficiently low that no significant dischargeis present across said space when the pressure inside said envelope isin a normal range,

(iii) said potential being sufficiently high to initiate a dischargeacross said space when the pressure inside said envelope is above saidnormal range,

(iv) current-responsive means connected in cir cuit with said highpotential-applying means and operable in response to a discharge beinginitiated across said space,

(v) and means responsive to initiation of an in terrupter-openingoperation for removing said high potential from across said space whenthe interrupter-opening operation is initiated and for reapplying saidhigh potential across said space when said interrupter is closed.

2. The monitoring means of claim 1 in which said means for removing saidhigh potential comprises:

(a) a switch connected in series with said high potential applyingmeans,

(b) means for closing said switch when the interrupter is closed,

(0) and means for opening said switch in response to initiation of aninterrupter-opening operation.

3. The apparatus of claim 1 in combination with:

(a) means for opening said contacts comprising an operation-initiatingmember movable through a predetermined travel before causing saidcontacts to separate,

(b) and means for removing said high potential in response to saidpredetermined travel before said contacts separate.

4. The interrupter of claim 1 in combination with interrupting meanscontrolled by said current-responsive means for interrupting the flow ofcurrent through said discharge upon operation of said current-responsivemeans.

5. In combination,

(a) a vacuum-type circuit interrupter comprising an evacuated envelope,a pair of relatively movable contacts inside the envelope, and a metalpart electrically isolated from said contacts when the interrupter isclosed by evacuated space inside said envelope,

(b) means for monitoring the pressure inside said evacuated envelopewhile the interrupter is carrying current therethrough, comprising:

(i) high potential-applying means for applying a high potential acrosssaid space between said metal part and said contacts when theinterrupter is closed,

(ii) said potential being sufliciently low that no significant dischargeis present across said space when the pressure inside said envelope isin a normal range,

(iii) said potential being sufiiciently high to initiate a dischargeacross said space when the pressure inside said envelope is above saidnormal range,

(iv) current-responsive means connected in circuit with said highpotential-applying means and operable in response to a discharge beinginitiated across said space,

(v) and means responsive to initiation of an interrupter-openingoperation for removing said high potential from across said space whenthe interrupter-opening operation is initiated and for reapplying saidhigh potential across said space when said interrupter is closed.

6. The monitoring means of claim 5 in which said means for removing saidhigh potential comprises:

(a) a switch connected in series with said high potential-applyingmeans,

(b) means for closing said switch when the interrupter is closed,

(c) and means for opening said switch in response to initiation of aninterrupter-opening operation.

References Cited UNITED STATES PATENTS 1,757,397 5/1930 Sorenson et al.200 -131 1,790,152 1/1931 Hull 317-62 X 1,819,154 8/1931 Eschholz200-144 1,972,362 9/1934 Sorenson 200-138 3,339,112 8/1967 Lee et a1317- X LEE T. HIX, Primary Examiner.

J. D. TRAMMELL, Assistant Examiner.

1. IN COMBINATION, (A) A VACUUM-TYPE, CIRCUIT INTERRUPTER COMPRISING ANEVACUATED ENVELOPE, A PAIR OF RELATIVELY MOVABLE CONTACTS INSIDE THEENVELOPE, AND A TUBULAR METAL SHIELD SURROUNDING THE CONTACTS ANDELECTRICALLY ISOLATED FROM SAID CONTACTS WHEN THE INTERRUPTER IS CLOSEDBY EVACUTED SPACED INSIDE SAID ENVELOPE, (B) MEANS FOR MONITORING THEPRESSURE INSIDE SAID EVACUATED ENVELOPE WHILE INTERRUPTER IS CARRYINGCURRENT THERETHROUGH, COMPRISING: (I) HIGH POTENTIAL-APPLYING MEANS FORAPPLYING A HIGH POTENTIAL ACROSS SAID SPACE BETWEEN SAID SHIELD AND SAIDCONTACTS WHEN THE INTERRUPTER IS CLOSED, (II) SAID POTENTIAL BEINGSUFFICIENTLY LOW THAT NO SIGNIFICANT DISCHARGE IS PRESENT ACROSS SAIDSPACE WHEN THE PRESSURE INSIDE SAID ENVELOPE IS IN A NORMAL RANGE, (III)SAID POTENTIAL BEING SUFFICIENTLY HIGH TO INITIATE A DISCHARGE ACROSSSAID SPACE WHEN THE PRESSURE INSIDE SAID ENVELOPE IS ABOVE SAID NORMALRANGE, (IV) CURRENT-RESPONSIVE MEANS CONNECTED IN CIRCUIT WITH SAID HIGHPOTENTIAL-APPLYING MEANS AND OPERABLE IN RESPONSE TO A DISCHARGE BEINGINITIATED ACROSS SAID SPACE, (V) AND MEANS RESPONSIVE TO INITIATION OFAN INTERRUPTER-OPENING OPERATION FOR REMOVING SAID HIGH POTENTIAL FROMACROSS SAID SPACE WHEN THE INTERRUPTER-OPENING OPERATION IS INITIATEDAND FOR REAPPLYING SAID HIGH POTENTIAL ACROSS SAID SPACE WHEN SAIDINTERRUPTER IS CLOSED.